Overlay error detection

Inactive Publication Date: 2006-03-07
KLA TENCOR CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Benefits of technology

[0015]Other aspects of the invention relate to processing of radiation data collected from the two structures of the target. After a two-dimensional image of the target has been obtained, at least one one-dimensional signal may be derived from the image and used for determining an overlay error between the two structures. Where the one-dimensional signal is derived by averaging data in the image, the signal-to-noise ratio may be improved.
[0016]In conventional processing of data in overlay error detection, only data in portions of images at or close to edges of objects such as boxes or bars are used and the system is strongly dependent on the quality and contrast of the images. Modern chemical mechanical polishing processes tend to reduce t

Problems solved by technology

When so integrated, any system for detecting overlay errors is subject to vibrations.
If the detection system requires scanning light beams across targets, vibrations may cause the position of the beams to shift over time.
Since the collection objective employed in conventional methods has a high numerical aperture, this necessarily means that it has a small depth of focus.
Since two measurements are required instead of one as in a “single grab” measurement, this adversely affects throughput and is disad

Method used

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Example

[0036]For simplicity in description, identical components are labeled by the same numerals in this application.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037]FIG. 1 is a cross-sectional view of a polychromatic (e.g. white light) or laser dark field imaging system to illustrate one embodiment of the invention. As shown in FIG. 1, the imaging system 20 includes a source (not shown) which supplies a laser beam 22 or a beam 22 of polychromatic radiation such as white light, where the beam 22 is reflected by a mirror 26 towards overlay target 24. Target 24 has two structures thereon: one on a current layer at a higher elevation than the other one on a previous layer. The two structures may be two gratings (they can also be the type that includes box(es) or bar(s), though not shown as such in FIG. 1), located on two different planes and are substantially parallel to the planes, where one of the two planes such as plane 34 (or any plane parallel thereto) may serve as a reference plane. Radia...

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Abstract

An overlay target with gratings thereon is illuminated and radiation scattered by the target is imaged onto detectors. A phase difference is then detected between the outputs of the detectors to find the mis-alignment error. In another aspect, an overlay target with gratings or box-in-box structures is illuminated and radiation scattered by the target is imaged onto detectors located away from the specular reflection direction of the illumination in a dark field detection scheme. Medium numerical aperture optics may be employed for collecting the radiation from the overlay target in a bright or dark field configuration so that the system has a larger depth of focus and so that the two structures of the target at different elevations can be measured accurately at the same time. Analytical functions are constructed for the grating type targets. By finding the phase difference between the two gratings at different elevations, misalignment errors can be detected. Analytical functions are constructed as a model for box-in-box type targets where data points away from the edges of the box or bars can be used in the curve fitting. Symmetrical functions are employed to further reduce noise.

Description

BACKGROUND OF THE INVENTION[0001]This invention relates in general to overlay error detection and, in particular, to an imaging system for detecting misalignment of two structures and methods for determining overlay errors.[0002]Overlay error measurement requires specially designed targets to be strategically placed at various locations, normally in the street area between dies, on the wafers for each process. The alignment of the two overlay targets from two consecutive processes is measured for a number of locations on the wafer and the overlay error map across the wafer is analyzed to provide misalignment information. This information may then be used for the alignment control of wafer processing equipment.[0003]A key process control parameter in the manufacturing of integrated circuits is the measurement of overlay target alignment between successive layers on a semiconductor wafer. If the two overlay targets are misaligned relative to each other, the electronic devices fabricat...

Claims

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Application Information

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IPC IPC(8): G01B11/00G01K9/00G01B11/27H01L21/027
CPCG03F7/70633G01B11/272
Inventor NIKOONAHAD, MEHRDADZHAO, GUOHENGSHCHEGROV, ANDREI V.TSAI, BEN
Owner KLA TENCOR CORP
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